Flow machine for a fluid with a radial sealing gap between stator parts and a rotor

ABSTRACT

Shown with the invention are self-supporting wear rings ( 1   a,    1   b ) for flow machines with a fluid, which are arranged at a radial sealing gap ( 18 ) to a rotor ( 9 ), and of which the outer jacket surface ( 3 ) is provided with a wear surface ( 2 ). The wear rings ( 1   a,    1   b ), which are fixed in the axial direction, consist of a material with lower thermal expansion coefficients than their support and lie hollowly on their inner jacket surface, with a first conical holder surface ( 8 ) encountering with the apex of its cone a second holder surface ( 8 ″), which is designed as straight shoulder, in the plane of the latter ( 19 ) on the axis of rotation or encountering a second holder surface, which is designed as a conical holder surface ( 8 ′), at its cone apex on the axis of rotation ( 20 ).

[0001] The invention relates to a flow machine for a fluid, comprising a radial sealing gap between stator parts and a rotor, with a self-supporting wear ring, of which the outer jacket surface is provided with a wear surface and which is axially fixed in the direction of the axis of rotation of the rotor, being provided at the sealing gap.

[0002] In flow machines, radial sealing gaps which are axially flowed through frequently arise between the rotating parts and the stator parts and must be kept small in order to keep leakage losses low. Many fluids are provided with solid parts which can lead to abrasive wear in such narrow sealing gaps. This is caused on the one hand by the rotation of the rotor and on the other hand by a pressure difference which is effective over the sealing gap in the axial direction. A widening of the sealing gap increases the loss flow and reduces the volumetric efficiency.

[0003] Up to a certain quota of solid parts one resorts to coating the surfaces in the sealing gap with a wear resistant protective coating, the lifetime of which is given through the nature of the operation. When the repair intervals become too short, therefore, there remains only the use of self-supporting wear rings of ceramic materials. These admittedly have a very high wear resistance, but are however constructionally difficult to handle, since they are rather brittle and can be manufactured only in simple shapes due to their wear resistance. A further disadvantage in comparison with other materials consists in their insufficient coefficients of thermal expansion in connection with their low elasticity, which represents a risk for the operator of a flow machine, such as for example a multistage radial pump, when a wear ring is stretched at its inner side. Temperature fluctuations in the flow medium, but also certain operating situations such as the forwarding against a closed slider, which can likewise lead to a temperature increase, can lead to impermissible tension stresses in a wear ring of this kind.

[0004] In a wear ring which is stretched at its outer jacket surface and the wear surface of which lies on the inner side, a lowering of the temperature results in a uniformly distributed increase of the compression stress, which is as a rule permissible. If rather higher temperatures are operated at, the outwardly held wear rings can be held in a shrink connection, which in spite of the greater thermal expansion of a holding metal part is still sufficient for the centering and the force transfer. The situation is different in wear rings which are provided with a wear surface on their outer jacket surface.

[0005] The object of the invention is to make wear rings with low coefficients of thermal expansion which are provided on their jacket surface with a wear surface in order to make them usable for flow machines in a large range. This object is satisfied by the characterizing part of the independent claim 1 in that the wear ring consists of a material with a lower thermal expansion than parts on which it is supported; in that it lies hollowly on its inner jacket surface up to a specific temperature intended for the sealing gap; and in that a first conical holder surface encounters with the apex of its cone a second holder surface, which is designed as a straight shoulder, in the plane of the latter on the axis of rotation or encounters a second holder surface, which is designed as a conical holder surface, at its cone apex on the axis of rotation.

[0006] This arrangement has the advantage that the conical holder surfaces, which expand to a greater extent than the wear ring when the temperature increases, expand along their cone jacket lines relative to the wear ring. If the axial bias force on the cone surfaces is not chosen too large—the wear ring also expands somewhat—then a minimum sliding movement between the conical surfaces can take place, which prevents excessive ring tensions in the form of tension stresses in the wear ring. With a straight shoulder as holder surface this minimum sliding movement is likewise possible. In the frictionless state a straight shoulder with an oppositely lying cone surface would also effect a centering of the wear ring with falling temperature. Due to the friction it can therefore be advantageous to additionally attach to the side of the straight shoulder an outer centering shoulder, the shrinking tension of which is still permissible at the lowest arising temperatures. In this way an exact centering at the straight shoulder in each temperature cycle is achieved.

[0007] This construction shows advantages in wear rings with a coefficient of thermal expansion a of less than 10×10⁻⁶ degrees C. Wear rings of highly wear resistant material such as ceramics, for example metal oxides, tungsten carbide or silicon carbide, can be used in this way. Even fluids with larger solid components can be forwarded. In this the diameter of individual solid parts can have the size of the gap width of the sealing gap, since a kind of grinding process for these large parts arises due to the choice of the wear rings. This process has a favorable effect at high operating temperatures above 100° C. and/or above 300° C., since ceramic materials change their wear properties only at much higher temperatures.

[0008] In the following the invention will be described with reference to exemplary embodiments. Shown are:

[0009]FIG. 1 schematically from the prior art, a section of a double-flow pump with wear rings which are shrunk in at rotors and stator parts;

[0010]FIG. 2 schematically, a section from FIG. 1, in which the leakage flows through the radial sealing gaps are illustrated;

[0011]FIG. 3 schematically and enlarged, a first embodiment in accordance with the invention for a wear ring at a rotor;

[0012]FIG. 4 schematically and enlarged, a further embodiment in accordance with the invention at a rotating sleeve;

[0013]FIG. 5 schematically and enlarged, a further embodiment in accordance with the invention with two conical holder surfaces;

[0014]FIG. 6 schematically and enlarged, a further embodiment in accordance with the invention at a stationary sleeve; and

[0015]FIG. 7 schematically, a further embodiment in accordance with the invention with two conical holder surfaces.

[0016] In the figures, self supporting wear rings 1 a, 1 b for flow machines with a fluid are shown, which are arranged at a radial sealing gap 18 to a rotor 9 and of which the outer jacket surface 3 is provided with a wear surface 2. The wear rings 1 a, 1 b, which are fixed in the axial direction, consist of a material with a lower coefficient of thermal expansion than their support and lie hollowly on their inner jacket surface, with a first conical holder surface 8 encountering with the apex of its cone a second holder surface 8″, which is designed as a straight shoulder, in the plane 19 of the latter on the axis of rotation or with a second holder surface, which is designed as a conical holder surface 8′, encountering the axis of rotation 20 at its cone apex.

[0017] In the following figures, the same reference symbols will be used for similar functional parts.

[0018] In FIG. 1 a known arrangement of a double-flow radial pump with closed rotors 4, 14, a housing 10 and stator parts 12 a, 12 b, 12 c, 12 d is shown. An inlet flow 15 flows through a first rotor 4, experiences a pressure increase and is conducted via a deflection passage 21 to a second rotor 14, and then after a further pressure increase leaves the housing 10 as outlet flow 17 via an outlet spiral 16. The rotor 9 with axis of rotation 20 is assembled from a shaft 11, rotors 4, 14 and shaft sleeves 22 a, 22 b, 22 c, 22 d. Bearings and housing seals are not shown.

[0019] Radial sealing gaps 18 are produced with shrunk in wear rings at the cover disc of the rotors 4, 14. In the first rotors 4, further sealing gaps 18 are provided behind the rotor at the hub side.

[0020] The enlarged section in FIG. 2 shows leakage flows 25, 24, 23, which flow back in accordance with the pressure gradient between the rotor 9 and the stator parts 12 c, 12 d. The back-flow amount is determined through the gap width of the radial sealing gaps 18. The latter consist of a counter ring 26 which is shrunk in a stator part 12 c, 12 d and of a wear ring 1 a, 1 b which is secured on the rotating part 4, 14 and of which the outer jacket surface is formed as a wear surface.

[0021] In FIG. 3 the wear ring 1 a is provided on its outer side with a cylindrical jacket surface 3 which is at the same time formed as a wear surface 2. The inner cylindrical jacket surface lies hollowly and forms a gap S to the rotor 4. The wear ring is supported in the axial direction at an end surface by a holder surface in the form of a straight shoulder 8″ which is perpendicular to the axis of rotation 20. On the opposite side a holder ring 5, which is in turn centered at the rotor 4 and is held by screws 6, presses the wear ring 1 a with a conical holder surface 8 in the axial direction. The conical surface 8 belongs to a cone with half cone angle β, with the apex of the cone encountering a plane 19, in which the straight shoulder 8″ lies, on the axis of rotation 20. In addition to the friction of the holder surfaces 8, 8″, a rotational securing 13 in the form of a pin which lies in a groove of the wear ring 1 a can transfer torque from the rotor 4 to the wear ring.

[0022] If it is assumed that the lowest operating temperature is present in the shown position, then the gap S should be dimensioned in such a manner that the gap S disappears at a specific operating temperature as a result of the greater thermal expansion of the rotor without impermissible tension stresses arising in the wear ring 1 a at the highest operating temperature.

[0023] If the plane 19 of the straight shoulder 8″ is taken as a starting basis in order to describe the movement during an increasing heating up of a point P which is common to the holder surface 8 and the wear ring 1 a, then the holder ring 5 expands in the axial direction proportionally to L×ΔT×α_(L), with L being the distance from the plane 19, ΔT the difference in temperature in degrees Celsius and α_(L) the coefficient of thermal expansion of the rotor 4. At the same time the holder ring expands relative to the axis of rotation 20 in the radial direction proportionally to R×ΔT×α_(L), with R being the radial distance from the point P. The rising of the point P thus amounts to: $\frac{R \times \Delta \quad T \times \alpha_{L}}{L \times \Delta \quad T \times \alpha_{L}} = {\frac{R}{L} = {{\tan \quad \beta} = {constant}}}$

[0024] Analogously the rising of the original point P can be determined for the wear ring 1 a with a coefficient of thermal expansion α_(v): $\frac{R \times \Delta \quad T \times \alpha_{V}}{L \times \Delta \quad T \times \alpha_{V}} = {\frac{R}{L} = {{\tan \quad \beta} = {constant}}}$

[0025] This means that the holder surface 8′ and the wear ring which is held by it move with different speeds on the same conical surface with the half cone angle β. If the friction between the holder surface 8 and the wear ring 1 a is dimensioned such that in the more rapid expansion of the holder ring and the rotor no impermissible tension stresses arise in the wear ring, then there exists a fixing which permits the temperature dependent displacement between the holder ring 5 or the rotor 4, respectively, and the wear ring. It is thus sufficient to design the holder screws 6 for example as necked-down bolts and tighten them in such a manner that no excessively large frictional forces can arise. A further aid in the mounting of the wear ring 1 a consists in an additional centering shoulder 7 which lies in contact at the outer jacket surface 3 of the wear ring at low temperatures and departs from it at increasing temperatures. As long as the angle β is not chosen to be too close to 90°, a continuous centering of the wear ring 1 a on the holder surface 8 of the holder ring 5 takes place.

[0026] In FIG. 4 the length L of a wear ring 1 b in relationship to the radial distance R is chosen to be greater than in FIG. 3. In this the half cone angle P becomes smaller and a better centering through the holder surface 8 takes place. Simultaneously with the improved centering a greater tension stress also arises in the wear ring 1 b. The pressing force on an oppositely lying holder surface 8″ of a holder ring 5 must therefore be matched to the spreading action of the cone.

[0027] In FIG. 5 the length of the wear ring 1 b is composed of two sub-lengths L₁ and L₂. Since the sum L₁+L₂ corresponds approximately to the radial distance R, well centering half cone angles β₁ and β2 are created. In relation to a theoretical separation plane E which is perpendicular to the axis of rotation 20 and passes through the intersection of the two cone apexes, two oppositely lying points P₁ and P₂ move in the holder surfaces 8 and 8′ with increasing temperature at the same radius on the respective conical surface.

[0028] There are constructional restrictions in which the length of the wear ring must be chosen substantially smaller than the radial distance R of the holder surfaces 8, 8′. Nevertheless it is possible to achieve a good centering, i.e. half cone angles β₁, β₂ of similar size for the wear ring 1 b if the point of contact of the two cone apexes is displaced relative to the wear ring on the axis of rotation 20 in a direction such as is shown in FIG. 7. There the theoretical separation plane E lies outside the wear ring. The effective length of the wear ring 1 b results from the difference L₂-L₁. The wear ring 1 b experiences a ring stress which is a compression stress through the holder surface 8 with the larger half cone angle β₁ and a ring stress which is a tension stress through the holder surface 8′ with the half cone angle β₂. The points P₁ and P₂ of the holder surfaces move along the cone surfaces in temperature fluctuations.

[0029] In FIG. 6 a wear ring 1 b is centered and secured analogously to FIG. 4, with the holder ring 5 and a stator part 12 b, at which a sleeve is molded on, forming non rotating holder surfaces 8 and 8″. A rotating counter ring 26 is held at the rotor 4 with holder screws 6′. This counter ring 26 can likewise consist of a ceramic and have conical holder surfaces, the cone apexes of which make contact on the axis of rotation 20. In temperature increases, the rotor 4 and the holder ring 5′ run off outwardly more rapidly with respect to the counter ring 26 on the cone surfaces with half cone angle γ₁, γ₂, and a gap arises at the outer jacket surface of the counter ring. Nevertheless a reasonable centering of the counter ring via the half cone angles γ₁, γ₂ is possible. At very large temperature differences or much greater coefficients of thermal expansion of the rotor 4 and the holder ring 5′ relative to the counter ring 26, this is likewise a conceivable solution, if the counter ring 26 can not remain shrunk in over the entire temperature range. 

1. Flow machine for a fluid, comprising a radial sealing gap (18) between stator parts (12 a, b, c, d) and a rotor (9), with a self-supporting wear ring (1 a, 1 b), of which the outer jacket surface (3) is provided with a wear surface (2) and which is axially fixed in the direction of the axis of rotation (20) of the rotor (9), being provided at the sealing gap, characterized in that the wear ring (1) consists of a material with a lower thermal expansion than parts (4, 14, 15) on which it is supported; in that it lies hollowly on its inner jacket surface up to a specific temperature which occurs for the sealing gap (18); and in that a first conical holder surface (8) encounters with the apex of its cone a second holder surface (8″), which is designed as straight shoulder, in the plane (19) of the latter on the axis of rotation or encounters a second holder surface (8), which is designed as a conical holder surface, at its cone apex on the axis of rotation (20).
 2. Flow machine in accordance with claim 1 , characterized in that the wear ring (1) is additionally outwardly centered at its jacket surface (3) at one side with a centering shoulder (7) at the lowest temperature occurring for the sealing gap (18).
 3. Flow machine in accordance with claim 1 or claim 2 , characterized in that the material of the wear ring has a coefficient of thermal expansion α of less than 10×10⁻⁶ degrees C.
 4. Flow machine in accordance with claim 3 , characterized in that the material of the wear ring consists of a ceramic such as for example metal oxides, tungsten carbide or silicon carbide.
 5. Use of a flow machine in accordance with any one of the claims 1 to 4 for a fluid which is provided with solids.
 6. Use of a flow machine in accordance with claim 5 for a fluid in which solid parts have a diameter of the order of magnitude of the radial sealing gap (18).
 7. Use of a flow machine in accordance with claim 5 for temperatures greater than 100 degrees C.
 8. Use of a flow machine in accordance with claim 5 for temperatures greater than 300 degrees C.
 9. Flow machine for a fluid, comprising a radial sealing gap (18) between stator parts (12 a, b, c, d) and a rotor (9), with a self-supporting counter ring (26), of which the inner jacket surface is provided with a wear surface (2′) and which is axially fixed in the direction of the axis of rotation (20) of the rotor (9), being provided at the sealing gap, characterized in that the counter ring (26) consists of a material with a lower thermal expansion than parts (4) on which it is supported; in that it lies hollowly on its outer jacket surface up to the lower temperatures which occur for the sealing gap (18); and in that a first conical holder surface (26 a) encounters with its cone apex a second conical holder surface (26 b) at its cone apex on the axis of rotation (20). 